The farmer’s canning application required executing a specific time vs. temperature profile to process the vegetables properly. The thermal control system is composed of the PID controller, solid-state relay (SSR), and 1,500W hotplate. Refer to Figure 1.

The Arduino controller that I eventually made stores a
number of time vs. temperature profiles (Figure 2). Once
programmed on a PC (in the normal Arduino IDE way),
the unit can be taken out to the process shed for stand-alone operation.

Hardware

This PID controller device consists of three sub-units:

Being a devoted nerd, I’ve
long been fascinated by
Proportional Integral
Derivative (PID) process
control. So, when a local
farmer asked me to
automate a vegetable
canning process, I took it as a challenge to physically realize a PID
temperature control device. Of course, many fine industrial process
controllers already exist (say, from Omega), but I strived to learn their secrets
and do it smaller and cheaper. The Arduino product family provides
inexpensive hardware for the home builder. Plus, the Arduino integrated
development environment (IDE) is easy to install and remarkably easy to use.

For these reasons, I decided to build an Arduino PID temperature control unit.